LAB Report Lathe Machine PDF

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EXPERIMENT TITLE U1 LATHE & MILLING MACHINE

ABSTRACT This experiment was conducted to familiarise ourselves with the tools that exist in the student workshop, namely the lathe tool and the milling tool. This is done by fabricating a specified component using both machines and learning from the process. For the lathe machine, the fabrication incorporates operations such as cutting, facing, centre drilling, plain turning, taper turning, knurling and chamfering. As for the milling machine, a V-block was made from a 92.2mm x 73.2mm x 49.2mm block of mild steel using manual feed and automatic feed. After the pieces were finished, they were compared with the schematics, and both pieces were within he tolerance limits. Important parameters were recorded and values such as material removal rate, feed and cutting speed were calculated. OBJECTIVE  

Part 1 – To fabricate a component using the lathe machine. Part 2 – To shape a V-Block using the milling machine.

INTRODUCTION Part 1: Lathe Machine Lathe machines are one of the oldest industrial machines in the manufacturing industry. Lathes operate by rotating a cylindrical object, commonly a metal workpiece, such that a tool may cut into it to produce a uniform axial pattern. The workpiece rotates on its axis but does not move in any other direction. The cutting tool is the moving part that advances along the path of desired cut. The lathe is quite a versatile equipment. With different attachments and slight modifications, it can be made to do operations such as turning, tapering, screw cutting, facing, knurling, dulling, spinning, grinding, polishing and boring. Out of those operations, the most basic and widely used one is turning. It involves cutting a workpiece into a specified diameter using a cutter fed perpendicular to the axis of rotation. If the tool was fed at an angle, tapering process or angled cuts can be done. (Virasak, 2016) Important pieces on the late include; Bed: It acts as the base of the machine. It is usually made of cast iron and the top surface must be machined accurately and precisely to avoid inaccuracies. Headstock: It is permanently mounted on the left side of the bed in the inner guideways and is supported by the leg. Inside it is a hollow spindle, as well as a mechanism to drive the spindle at several speeds. Spindle: It rotates on two large bearings located in the headstock casting. Tailstock: It is located on the inner guideways at the right side of the bed, opposite to the headstock. It is mostly for support, but it can be used to drill centre holes and other operations. Carriage: It is located between the headstock and tailstock on the lathe bed guideways. It carries the tool post and is used to modify the position of the cutting tool. 1

Lead screw: It is a long and threaded shaft used as the master screw. It is used during threading, to move the carriage a specific distance and produce an accurate thread. Feed rod: It is located parallel to the lead screw, and on the front side of the bed relative to it. It is a long shaft which has a key way along its length. It acts as a power transmission mechanism which is also used to move the carriage precisely along the longitudinal axis of the lathe.

Figure 1: A typical Lathe Machine with important parts labelled (Deb, n.d.)

Part 2: Milling Machine Milling machines are industrial machines used to remove material from a workpiece. This is done by using rotating cutters that are strong and sharp enough to cut through metallic workpieces. In the modern industry this process is mostly automated, and due to the large selection of drill bits and milling ends, it is capable to fabricate almost anything using the milling process, such as gun parts, circuit boards, jewellery and many more. There are two common modes of milling, which are face milling and end milling (cgstools.com, 2017) The most common milling operation would be face milling and it can be performed using a large selection of different tools. Usually cutters with a 45º entering angle are most frequently used, but there are other cutters used in different conditions such as round insert cutters, square shoulder cutters and side and face mills. End milling on the other hand mainly differs from face milling processes because of the type of tools that is used for cutting a given material. End mills have cutting teeth on the sides and ends of the mill, quite different to cutters and drill bits. Important pieces on the milling machine include; Head (Drive): It converts electrical power from the motor to mechanical power in the spindle. Drive system also allows the operator to change the cutting tool speed by changing the spindle speed (RPM). Quill: It contains the spindle, in which cutting tools are installed. It moved vertically in the head.

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Quill feed hand wheel: It moves the quill up and down within the head, same as the quill feed lever. Knee: It moves up and down by sliding on ways that are parallel to the column. Column: Its main function is to hold the turret. Turret: It allows the milling head to be rotated around the column's centre. Overarm (ram): It slides on the turret and allows the milling head to be repositioned over the table. Longitudinal traverse hand wheel: It moves the worktable in the left and right direction Cross traverse hand wheel: It moves the worktable in and out of the machine. Vertical movement crank: It moves the knee, saddle, and worktable up and down in unison.

Figure 2: A typical Milling Machine with important parts labelled (kanabco.com, 2018)

THEORETICAL BACKGROUND Since both lathe and milling machines are rotational cutting machines, they share mostly the same equations for the parameters. Rotational Speed (N) is usually given, but can be calculated by: 3

N=vπ D o v = Cutting Speed Do = Original Diameter Feed rate is the rate at which the table or cutting tool moves. It is conventionally measured in the unit of mm per revolution. It can be found by the equation:

f=

Length of cut 1 x N = Rotational Speed (RPM) Time of cut N

For the depth of cut (d), it can be measured or calculated as follows:

d=

Do − Df 2

Do = Original Diameter Df = Final Diameter

Material removal rate, measured in cm3/min, was calculated using the formula:

For lathe:

MRR=¿

(feed rate) x (rotational speed) x (removed area)

cm rev x xc m 2 rev min

= =

fNπ ( r2i −r 2f ) ¿ units of

c m3 min

f = Feed (Dist./Rev.) N = Rotational Speed (RPM) ri = Initial radius rf = Final radius

For milling a block face:

MRR=

Volume Time of cut

4

¿

d xw x l Time of cut

d = depth of cut w = width of face l = length of face

EXPERIMENTAL SETUP AND PROCEDURE Part 1: Lathe Machine

5



Machine Tools used: Lathe Machine, Specification: H.P. =0.75 H.P, overall length 1600-2000 mm, Swing Diameter =455-575 mm.



List of tools: Engg Steel Rule 6”, Outside calliper, Vernier callipers, Flat smooth file, Single point cutting tool, Knurling tool, Center drill, Drill chuck ½”, Spanner set, Parting off or necking tool, Thread gauge, Threading tool, Parting tool, Lathe Dog carrier etc.



Materials Used: Mild steel Bar (40 mm dia.)

 Procedure: 1. The workpiece drawing was analysed and understood thoroughly before planning the job. 2. A 130mm long piece was cut from 40 mm diameter bar. 3. The workpiece was held in the Lathe chuck and facing and centre drill operations were performed. The same procedure was repeated on the other side. 4. The workpiece was held in between live and dead centres. 5. Plain turning was performed (L=35mm), and chamfering and knurling operations on one side and the faces were interchanged axially. 6. Plane turning was performed by swivelling the compound rest at an angle of 4° 7. The threading was done by setting the levers per requirement. 8. Filing was done on the workpiece to smoothen the rough edges. 9. The workpiece was taken off the lathe and oiling was done to protect it from dust.  1. 2. 3. 4. 5. 6. 7.

Safety Precautions Loose clothes must not be worn while working on the machine. Work piece should be held tightly between the live and dead centres. Machine must be cleaned before use. Cutting tools should be held tightly in the tool holder. Clothes and hands must not come in contact with the revolving chuck, pulleys etc. The chips must not be touched when machine is removing them. Large feed must not be given to the cutting tool.



Drawing:

Figure 3: Drawing of the finished workpiece for lathe machine. Part 2: Milling Machine 

Apparatus: Milling machine and shaper machine. 6



Tools and Instruments: Vernier calliper, vernier height gauge, surface plate, side cutter, shaper cutting tools.



Material: Mild steel rectangular block size (92.2 x73.2 x 49.2) mm

 Procedure: 1. The work piece was fixed on the shaper vice and all the faces were finished according to the given dimensions 90 mm x 70mm x 48 mm 2. A centre line was marked on Surface plate with the help of a height gauge. 3. Two parallel lines were marked on 19 mm distance on both sides of centre line by referring to centre line mark. 4. The work piece was clamped again on shaper machine vice and a slot of 4 mm wide and 20 mm deep was made at the centre of top surface. 5. The machine was stopped and the tool head was swung counter-clockwise at the angle of 45° and then it was machined until the required depth. 6. The tool head was again swung counter-clockwise direction. 7. At an angle of 45° the other side of centre was machined until the required depth. 8. The zero position of tool head was set and the slotting was started until the 2mm deep and 4mm wide. 9. With help of surface plate and height gauge a slot of 10mm wide 2mm deep was marked at the distance of 15mm from top to bottom on both side of work piece. 10. Next a centre was marked on bottom surface then two Parallel lines were marked at the distance of 12 mm from centre line. 11. Ten the work piece was clamped on milling machine with the help of side milling cutter a slot of 10 mm wide x 2mm deep x 85mm Long was made. After completion, it was repeated on the other side. 12. A slot of 24mm deep was made on the bottom surface on whole length of the surface and sharp edges were removed with the help of smooth file.  1. 2. 3.

Safety precautions: The sharpness of milling cutters must not be checked with hands. The cutter must not be touched during machining. Over feeding must be avoided, as it may cause the damage of cutter and then accident may occur in result. 4. During machining on shaper, user must not stand in from of the machine because the hot chips may cause serious injury. 5. The nozzle of coolant must be set at proper position to avoid over heating of cutter and work. 6. The marking on work piece must be cleaned which may result in an error.



Drawing:

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Figure 4: Drawing of the finished workpiece for milling machine.

RESULTS AND DISCUSSION 8

Part 1: Lathe Machine

Figure 5: Final Part 1 workpiece after finishing all the lathe steps.



Notable Parameters

N, Feed rate, cutting speed and depth of cut are the notable parameters.



N (rpm): Table 1: RPM for different activities Activity

Plain Turning Knurling Threading

N (Code) 630 (RLY) 63 (SIY) 100 (JQY)

Separate values of N, or RPM are used for separate activities. The RPM related to each activity was given by the technician, along with the code needed to be set on the lathe machine to achieve said RPM.



Feed rate:

Table 2: Three data samples taken during different parts of the machine’s operation Operation Length of cut Time of cut (s) Feed rate, (mm) (mm/rev) 1. Rough Turning 1 35.0 20.9 0.519 2. Rough Turning 2 35.0 30.4 0.110 3. Finish Turning 35.0 45.0 0.074 4. Knurling 5.0 10.51 0.045

f

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The feeding procedure was done manually except for a few select cases, thus the feed rate varies significantly depending on the section and the operator. The values are calculated in standard units (mm per revolution). Note the low feed rate for knurling. This is to ensure an accurate pattern is formed on the workpiece. Finish turning also has lower feed rate to enhance the surface finish. Example calculation, Feed

rate

for

Rough

Turning

1

(mm/rev)

=

Length of cut 35 mm 630 rev =0.159 mm / rev ÷N= ÷ 60 s Time of cut 20.9 s 

Cutting Speed:

Table 3: data and cutting speeds for five separate activities in standard units (m/min) Operation N (RPM) Depth of cut, d Diameter (mm) Cutting speed, v (mm) (m/min) 1. Rough Turning 1 630 0.5 38.9 76.99 2. Rough Turning 2 630 0.5 38.4 76.00 3. Finish Turning 630 0.4 38.02 75.24 4. Knurling 63 38.02 7.525 5. Threading 100 25.0 7.853 Logically, the cutting speed decreases with smaller diameter because the circumference decreases. Example calculation, Cutting speed for Rough Turning 1 (m/min) =

π (0.0389)m 630rev πd m x x N= 1 min 1 rev 1rev

= 76.99

m/min



Material Removal Rate

Table 4: data and material removal rate for three applicable activities in standard units (cm3/min). Operation N, Initial Final Depth of Feed rate, MRR (RPM) Diamete Diameter cut (mm) f (mm/rev) (cm3/min) r (mm) (mm) 1. Rough Turning 630 39.4 38.9 0.5 0.519 10.05 1 2. Rough Turning 630 38.9 38.4 0.5 0.110 2.10 2 3. Finish Turning 630 38.4 38.02 0.4 0.074 1.06 Example calculation, Material Removal Rate for Rough Turning 1 (m/min) =

(

¿ π 0.0519

πfN ( r i −r f ) 2

)(

2

)

cm rev 630 ( 1.97 2−1.9452 ) c m 2 rev min 10

= 10.05 cm3/min 

Quality measurements:

Quality measurements were made using the Vernier Calliper. The dimensions of the workpiece must be within the tolerance limit specified in the specifications. For example, one of the diameters specified must be 38 mm +-0.5mm, while the achieved diameter was 38.02 mm. This measurement determined by the diameter was within the tolerance limit. Another quality measurement tool is the thread gauge, which is used to check the thread count and pitch of the workpiece. The workpiece has successfully passed the test of 2mm thread as specified. 

Control parameters to improve surface roughness:

The most important parameter to control to achieve smooth surface roughness would be the feed rate. A slower feed rate produces a smoother surface finish. Another factor to consider is the depth of cut. For finish turning, a smaller depth of cut would produce an overall smoother surface finish. This is because less resistance is encountered by the cutting tool as it cuts through the workpiece. However too light of a depth of cut may cause rubbing instead of cutting (Thompson, 2012).

Part 2: Milling Machine

Figure 6: Final Part 2workpiece after finishing all the milling steps. 

Critical Issues when using two machines

One problem that occurred when using two machines was the increase in safety hazards when transferring the workpiece from one machine to the other. Every time the workpiece needed to be transferred, the machine must be turned off and several safety measures must be taken. The operators must have their hands in the work area and risk injuring them. The operators also must move multiple times between machines, and because the floor was covered in excess lubricant, there are more chances of slipping and injury.



Can we machine the component using a single machine? What are the problems?

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It is possible, but this brings a new set of problems. Firstly, it will be inefficient to position the workpiece holders at 45° and back to flat multiple times. Having two separate machines set to flat angle and 45° angle optimises the workflow, making the fabrication process faster. Secondly, once the workpiece holders are angled and set, it will take a lot of effort to return it to the original state. Because of this, the workpiece must be exactly the right shape before angling the holders. Otherwise it will require the holders to be changed back and forth multiple times. Ultimately this means less flexibility is allowed in the fabrication process, as even small errors will significantly hinder the process.



Calculate the time taken, control parameters, cut quality and Material Removal Rate. 1. Time Taken

According to the demonstrator, the overall time it would take to completely finish the model is more than 4 hours. The demonstrator himself took 1 day to create the sample piece with high accuracy. Since we only had 2 hours, the workpiece was not completely finished within the time given. For subsequent groups doing this experiment after us, the length of the workpiece was significantly shortened. This allows the workpiece to be finished within the 2 hour limit of the session.

2. Control parameters Control parameters include: N (RPM), depth of cut, feed rate, material removal rate Table 5: data for milling of the side face from 72.8 mm to 70.45 mm Feed rate, f MRR Milling (mm N (RPM) Depth of Length of Time of (mm/min) to mm) cut (mm) cut (mm) cut (s) (cm3/min) 72.8 to 71.8 205 1.0 90 136 0.194 2.03 71.8 to 70.8 205 1.0 90 165 0.160 1.67 70.8 to 70.45 205 0.35 90 119 0.221 0.58 All of these values were not constant for each stage, thus one scenario (cutting from 72.8mm to 70.45 mm) was chosen for study.

Example calculation, Feed rate =

Length of cut 90 mm 205 rev ÷N= ÷ =0.194 mm /rev Time of cut 136 s 60 s

Material Removal Rate =

Volume Time of cut

12

=

depthof cut x length x width Time of cut

=

( 0.1 x 4.94 x 9.30 ) c m 3 60 s x 136 s 1 min

= 2.03 cm3/min

3. Cut quality Better cut quality was achieved by slowing down the feed rate and decreasing the depth of cut. For accuracy in measurement, the workpiece was filed using an iron filing and then cleaned using compressed air.

CONCLUSION After undergoing both lathe and milling processes, it can be concluded that when a smooth surface finish is desired, the feed rate must be reduced and the depth of cut must also be decreased. This is to reduce the amount of resistance the cutter encounters during operation. Even though the workpiece could not be finished until the end for Part 1, there were many things to learn from the operations that were managed to be done. Overall, through these activities, we have learnt the basic skillsets needed to operate these machines in the student workshop.

REFERENCES Cgstool.com (n.d.). What is End Milling?, Retrieved http://www.cgstool.com/blog/what-is-end-milling/ Deb,

March

R. (n.d.). Lathe Machine. Retrieved March https://sites.google.com/site/drrajdeepdeb/lath-machine

19,

19,

2018, 2018,

from from

Thompson, J. (2012, October 15). 10 Tips to Improve Surface Finish. Retrieved March 19, 2018, from https://www.canadianmetalworking.com/article/management/10-tips-toimprove-surface finish Virasak , L. (2016). Manufacturing Processes 4-5. Retrieved on March 19, 2018, from https://openoregon.pressbooks.pub/manufacturingprocesses45/chapter/unit-2-speedand-feed/

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